The present invention relates to devices for securing the edge of a stretched sheet and is applicable more particularly to securing the lower edge of a tent canvas of a light shelter of a general pyramidal shape, as well as a light shelter of this type having such a canvas securing device.
Light shelters are known having a metal supporting structure on which a tent canvas of general pyramidal shape is secured and stretched. The base of the pyramid formed by the stretched canvas is generally fixed to the structure by means of a lacing member passing through eyelets fixed to the lower edge of the canvas and secured to the metal supporting structure. Such a method of fixing has the obvious drawback of providing such fixing only at spaced apart points, which adversely affects the resistance of the canvas covering.
For fixing the lower edge of the canvas a relatively rigid beading can also be provided on two parallel sides of this edge, and the two parallel beadings are slid into longitudinal grooves formed in extruded light alloy sections. Each groove opens to the outside through a relatively narrow slit, through which only the canvas may pass so that each bead is thus held in the groove of a section once introduced therein through one of its ends.
Other devices are also known for fixing a canvas in an extruded section having a longitudinal groove, by transverse engagement of this canvas in the groove. Such a device is described for example in the U.S. Pat. No. 3,811,454. This device has a horizontal extruded section with a groove opening into one of its vertical faces through an inlet slit of a width less than that of the bottom of the groove and a locking rod being engageable transversally in the groove through its inlet slit and being immobilized therein so as to retain the edge of the sheet having a bead. The inlet slit of the groove of the section is defined by a first upper lip of small height and a second lower lip of great height, these two lips thus defining, therebehind and on each side of the inlet slit respectively, on the side of the first upper lip, a first shallow channel and on the side of the second lower lip a second deeper channel. The locking rod has a thickness less than the width of the inlet slit so that it can be inserted in the groove. It comprises a rib which is jammed in the locked position in the first channel, the sheet and the bead then being jammed in the second channel and the locking rod extends between the bead and the sheet housed in the second channel, on the one hand, and the first channel on the other. The locking rod which is inserted in the groove of the extruded section in the horizontal position and which remains in this position when locked, then bears by the upper part of its external face against the internal face of the upper lip of the groove, but by a flat face opposite this face against the upper face of the lip via the locked sheet. Such a canvas fixing device, although it has the advantage of being convenient to use because the canvas is inserted transversally into the groove of the section, is however not suitable for applications in which the canvas is subjected to very high tensile forces, as is the case for a tent canvas of a light shelter currently constructed. In fact, when the locked sheet is subjected to a high pulling force, this force may cause the sheet and the rod to be pulled out of the section.